Edge light type backlight unit

ABSTRACT

An edge light type backlight unit includes: a light source; a light guide plate which has an end surface, on which light emitted from the light source is incident, and propagates the light incident from the end surface; a rear-side reflective plate which is disposed on a surface side of the light guide plate; a perforated reflective plate which is disposed on a surface side of the light guide plate and has a plurality of fine holes, which penetrate from a surface on the light guide plate side to an emission-side surface facing the light guide plate-side surface and transmit light, and in which both the surface and the surface are reflection surfaces and a depolarization degree of the surface is 60% or less; and a circular polarization reflection film which is disposed on the surface side of the perforated reflective plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International Application No. PCT/JP2016/005187 filed Dec. 20, 2016, which was published under PCT Article 21(2) in Japanese, and which claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2015-253914, filed Dec. 25, 2015. The above applications are hereby expressly incorporated by reference, in their entirety, into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit used for a liquid crystal display and particularly relates to an edge light type backlight unit.

2. Description of the Related Art

Since a liquid crystal display (hereinafter, also referred to as an LCD) has a low power consumption and can be used as a space-saving image display device, the applications thereof have been expanding year by year. For example, the liquid crystal display is configured such that a backlight unit, a backlight-side polarizing plate, a liquid crystal panel, and a viewing side polarizing plate are provided in this order.

As a backlight unit, a direct backlight unit which includes a light source disposed below an emission surface thereof or an edge light type backlight unit (also referred to as a side light type backlight unit in some cases) which includes a light source disposed on a side of an emission surface thereof has been known.

A backlight unit has a great impact on the performance of an LCD such as the luminance or visibility of an image. Accordingly, various suggestions for improving the luminance of light (backlight) emitted by a backlight unit have been made.

For example, it has been suggested that a reflective polarizing plate is used as a film for improving the luminance A reflective polarizing plate transmits predetermined polarized light and reflects polarized light other than the predetermined polarized light. In a case where a reflective polarizing plate is used, the reflective polarizing plate transmits only linearly polarized light responding to a backlight-side polarizing plate, allows the transmitted light to be incident on the backlight-side polarizing plate, reflects polarized light other than the linearly polarized light so that retroreflection is repeated in a backlight unit, and allows the reflected light to be incident on the reflective polarizing plate again so that the light can be reused.

For example, JP1998-3079A (JP-H10-3079A) describes a backlight unit that uses a reflective polarizing plate reflecting circular polarization in a predetermined direction and transmitting other circular polarization due to a cholesteric liquid crystal. In this backlight unit, the circular polarization transmitted through the reflective polarizing plate is allowed to be incident on a λ/4 plate and then to be incident on a backlight-side polarizing plate as linearly polarized light in a predetermined direction.

While the circular polarization reflected by the reflective polarizing plate that separates circular polarization is reflected in the backlight, a change in polarizability, for example, change of right circular polarization into left circular polarization, is shown. In a case where this circular polarization is incident on a reflective polarizing plate that uses a cholesteric liquid crystal layer again, the circular polarization is transmitted through the reflective polarizing plate. In other words, by using the reflective polarizing plate that reflects circular polarization, almost all light can be efficiently used through the extremely small number (one to several times) of times of reflection.

JP2015-518259A discloses a configuration of an edge light type backlight unit which uses a light guide box having a cavity therein without including a light guide plate as a configuration of a backlight unit that is capable of uniformizing light intensity distribution in the plane of emitted light and has attempted weight reduction and cost reduction. The light guide box guides light between a reflection sheet provided on one surface thereof and a light leakage sheet facing the reflection sheet and having a plurality of light leakage holes provided in a light emission opening of the light guide box. The surface of the light leakage sheet on the light guide box side is a reflection surface and the surface on the opposite side is an irregular reflection surface.

SUMMARY OF THE INVENTION

By using a reflective polarizing plate which transmits polarized light in a predetermined state and reflects other polarized light as described in JP1998-3079A (JP-H10-3079A) in a backlight unit used in an LCD, utilization efficiency of light is improved so that the luminance of light to be incident on a liquid crystal panel can be improved.

Further, in JP2015-518259A, the light intensity can be uniformized and weight reduction is achieved, but there is a problem in that a support frame structure for supporting the light leakage sheet at a position of an opening portion of the light guide box is complicated so that the thickness of the light guide box is unlikely to be reduced.

In recent years, further improvement of the luminance of light to be incident on a liquid crystal panel has been required for various reasons such as a decrease in luminance of a display image caused by a decrease in opening ratio of a pixel due to improvement of high definition of an LCD. Further, reduction of the thickness of an LCD has been also required at the same time.

The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide an edge light type backlight unit which is used for an LCD or the like, is capable of emitting light (backlight) with high luminance by further improving light utilization efficiency, and can be configured to be thin.

There is provided an edge light type backlight unit comprising: a light source; a light guide plate which has an end surface, on which light emitted from the light source is incident, and propagates the light incident from the end surface; a rear-side reflective plate which is disposed on a first principal surface side of the light guide plate; a perforated reflective plate which is disposed on a second principal surface side of the light guide plate facing the first principal surface so as to face the rear-side reflective plate and has a plurality of fine holes, which penetrate from a light guide plate-side surface to an emission-side surface facing the light guide plate-side surface and transmit light, and in which both the light guide plate-side surface and the emission-side surface are reflection surfaces and a depolarization degree of the emission-side surface is 60% or less; and a circular polarization reflection film which is disposed on the emission-side surface side of the perforated reflective plate.

The “depolarization degree” in the present invention is measured on a flat reflection surface that does not have fine holes. A method of measuring the depolarization degree will be described below.

The “fine hole” indicates a through-hole having an opening diameter of 1 mm or less.

Further, in a case where the emission surface of the backlight unit is set as the surface, the “rear surface” in the rear-side reflective plate indicates the rear surface of the backlight unit which faces the surface.

In the edge light type backlight unit according to the present invention, it is preferable that the depolarization degree of the light guide plate-side surface of the perforated reflective plate is 90% or greater.

In the edge light type backlight unit according to the present invention, it is preferable that the emission-side surface of the perforated reflective plate is a specular reflection surface.

In the edge light type backlight unit according to the present invention, it is preferable that an area ratio of openings of the fine holes in the emission-side surface of the perforated reflective plate is in a range of 10% to 50%.

In the edge light type backlight unit according to the present invention, it is preferable that a ratio of a thickness of the perforated reflective plate to an opening diameter of the fine holes in the emission-side surface of the perforated reflective plate is 2 or greater.

In the edge light type backlight unit according to the present invention, the openings of the fine holes of the perforated reflective plate on the light guide plate-side surface respectively may have a lens.

In the edge light type backlight unit according to the present invention, the circular polarization reflection film may be formed of a λ/4 film and a linearly polarized light reflection film which are disposed in order from the perforated reflective plate side and may include a cholesteric liquid crystal layer.

In the edge light type backlight unit according to the present invention, a wavelength conversion layer which receives light from the light source and emits light having a wavelength different from that of the light may be provided between the light source and the perforated reflective plate.

The edge light type backlight unit of the present invention includes: a light source; a light guide plate which has an end surface, on which light emitted from the light source is incident, and propagates the light incident from the end surface; a rear-side reflective plate which is disposed on a first principal surface side of the light guide plate; a perforated reflective plate which is disposed on a second principal surface side of the light guide plate facing the first principal surface so as to face the rear-side reflective plate and has a plurality of fine holes, which penetrate from a light guide plate-side surface to an emission-side surface facing the light guide plate-side surface and transmit light, and in which both the light guide plate-side surface and the emission-side surface are reflection surfaces and a depolarization degree of the emission-side surface is 60% or less; and a circular polarization reflection film which is disposed on the emission-side surface side of the perforated reflective plate. Due to this configuration, it is possible to realize reduction of the thickness and emit light (backlight) with high luminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view schematically illustrating the configuration of a backlight unit according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view illustrating an emission surface side of a perforated reflective plate.

FIG. 3 is a schematic cross-sectional view illustrating a design change example 1 of the backlight unit according to the first embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a design change example 2 of the backlight unit according to the first embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating a design change example 3 of the backlight unit according to the first embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view schematically illustrating the configuration of a backlight unit according to a second embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view schematically illustrating the configuration of a backlight unit according to a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of a backlight unit of the present invention will be described with reference to the accompanying drawings.

In the present specification, the numerical ranges expressed using “to” indicate the ranges including the numerical values described before and after “to” as the lower limits and the upper limits.

The edge light type backlight unit of the present invention is mainly used for a liquid crystal display (LCD). In an LCD, the edge light type backlight unit is used for emitting light (backlight) for displaying an image to a liquid crystal panel formed by arranging liquid crystal cells (liquid crystal pixels).

FIG. 1 is a schematic cross-sectional view schematically illustrating the configuration of an edge light type backlight unit according to a first embodiment of the present invention.

A backlight unit 10 of the present embodiment illustrated in FIG. 1 includes: a light source 14; a light guide plate which has an end surface 16 a, on which light emitted from the light source 14 is incident, and propagates the light incident from the end surface 16 a; a rear-side reflective plate 12 which is disposed on a first principal surface 16 b side of the light guide plate 16; a perforated reflective plate 20 which is disposed on a second principal surface 16 c side facing the first principal surface 16 b of the light guide plate 16 and is disposed to face the rear-side reflective plate 12; and a circular polarization reflection film 30 which is disposed on a surface 22 side of the perforated reflective plate 20 opposite to a side of the light guide plate 16.

The perforated reflective plate 20 has a plurality of fine holes 24 which penetrate from a surface 21 on the light guide plate 16 side to the emission-side surface 22 facing the surface 21 on the light guide plate 16 side and transmit light and in which both the light guide plate-side surface 21 and the emission-side surface 22 are reflection surfaces and a depolarization degree of the emission-side surface 22 is 60% or less. Hereinafter, the light guide plate-side surface 21 of the perforated reflective plate 20 is referred to as a light guide plate-side reflection surface 21 and the emission-side surface 22 is referred to as an emission-side reflection surface 22.

An optical member indicated by the dashed line in FIG. 1 is a backlight-side polarizing plate 39 which is typically provided in an LCD and used for converting light incident on a liquid crystal panel into predetermined linearly polarized light.

In the backlight unit 10, light L emitted from the light source 14 is incident on an end surface 16 a of the light guide plate 16, transmitted through the fine holes 24 of the perforated reflective plate 20, and emitted from the opening 24 a on the circular polarization reflection film 30 side while total reflection is repeatedly guided between the first principal surface 16 b and the second principal surface 16 c in the light guide plate 16. Further, the light L emitted from the openings 24 a is incident on the circular polarization reflection film 30.

In the light L which has been incident on the circular polarization reflection film 30, circular polarization having a predetermined orientation (here, left circular polarization L_(L)) is reflected by an action of the circular polarization reflection film 30. Further, in the light L which has been incident on the circular polarization reflection film 30, other circular polarization (here, right circular polarization L_(R)) components are emitted as linearly polarized light (this will be referred to as first linearly polarized light L₁) having an orientation of being transmitted through the backlight-side polarizing plate 39 through the circular polarization reflection film 30. Further, the left circular polarization LL reflected by the circular polarization reflection film 30 is reflected by the emission-side reflection surface 22 of the perforated reflective plate 20 and then converted into the right circular polarization L_(R) for reuse. By reusing the reflected light, light with high luminance can be allowed to be incident on the backlight-side polarizing plate 39 (liquid crystal panel).

In the present example, the circular polarization reflection film 30 has a λ/4 film 32 and a linearly polarized light reflection film 34, disposed in this order from the perforated reflective plate 20 side, which transmits first linearly polarized light L₁ and reflects second linearly polarized light L₂ orthogonal to the first linearly polarized light L₁. Therefore, light incident on the circular polarization reflection film 30 is incident on the linearly polarized light reflection film 34 through the λ/4 film 32, the first linearly polarized light L₁ is transmitted through the linearly polarized light reflection film 34, and the second linearly polarized light L₂ is reflected. Further, the second linearly polarized light L₂ is incident on the λ/4 film 32 again and emitted to the perforated reflective plate 20 side as circular polarization (left circular polarization L_(L)) in a predetermined direction. The left circular polarization LL is converted into right circular polarization L_(R) after being reflected by the emission-side reflection surface 22 of the perforated reflective plate 20, converted into first linearly polarized light L₁ due to the action of λ/4 during transmission through the λ/4 film 32 again, and then emitted.

The fine holes 24 provided in the perforated reflective plate 20 may have light-transmitting properties of transmitting light L and the inside of the holes 24 may be a space or may be filled with a transparent material that is transparent with respect to light. Here, “having light-transmitting properties” means that the light transmittance with respect to an incidence ray is 60% or greater.

FIG. 2 is a plan view illustrating the emission-side reflection surface 22 of the perforated reflective plate 20 when seen from the normal direction. The perforated reflective plate 20 is formed by providing a plurality of through-holes (fine holes) having a predetermined size at a predetermined pitch on a rectangular plate having a predetermined thickness. In FIG. 2, the two-dimensional arrangement of the fine holes 24 is an arrangement in which an even matrix and an odd matrix are shifted at a half pitch (so-called staggered arrangement), but the arrangement and the arrangement pitch of the fine holes 24 are not particularly limited. The arrangement of the fine holes 24 is not limited to the arrangement illustrated in FIG. 2 and may be a matrix arrangement (so-called lattice form arrangement) in which the even matrix and the odd matrix match each other or are in an random arrangement. Further, in order to make the luminance in the emission surface uniform, the fine holes 24 may be arranged in in-plane distribution by considering the distance between the fine holes 24 and the light source 14. For example, the fine holes may be formed such that the density thereof increases as the fine holes are separated from the light source position or the opening diameter thereof increases. Further, the arrangement pitch of the fine holes 24 may be as fine as possible, and the distance of fine holes adjacent to each other is preferably in a range of 0.01 to 1.0 mm.

The fine hole 24 may be formed vertically or obliquely to the reflection surfaces 21 and 22 of the perforated reflective plate 20. The shapes of the openings 24 a and 24 b of the fine hole 24 are not particularly limited and may be an ellipse, an arc, or a polygon without limitation to a circle. Further, the shapes of the openings 24 a and 24 b of the fine hole 24 may be the same as or different from each other. It is preferable that the fine hole 24 is a through-hole in which the shape of a cross section in parallel with the reflection surfaces 21 and 22 is a column (alternatively, an oblique column) that matches the shape of the openings, but one fine hole may be formed at a position with a different thickness and a different cross-sectional shape. Further, the fine hole 24 may have a shape in which the opening diameter gradually decreases toward the emission-side reflection surface 22 from the light guide plate-side reflection surface 21 side.

In a case where the thickness of the perforated reflective plate 20 is set as t and the opening diameter of the fine hole 24 in the emission-side reflection surface 22 is set as d, it is preferable that the ratio t/d of the thickness t to the opening diameter d satisfies an expression of “2≤t/d”. In other words, it is preferable that the thickness t of the perforated reflective plate 20 is twice or more the opening diameter of the fine hole 24. It is more preferable that an expression of “2≤t/d≤5” is satisfied.

Further, the opening diameter d is a diameter of a circle in a case where the opening 24 a has a circular shape. The opening diameter d is a diameter (equivalent circle diameter) of a circle with the same area as the opening area in a case where the opening 24 a does not have a circular shape.

The opening diameter d of the fine hole 24 is not particularly limited. For example, the opening diameter d may be set to 1 mm or less or 0.1 mm or less.

The light guide plate-side reflection surface 21 of the perforated reflective plate 20 may be a reflection surface that efficiently reflects light incident from the light source 14 side and the depolarization degree thereof is not particularly limited. Here, the region that functions as a reflection surface is a region excluding the openings 24 b of the fine holes 24 from the light guide plate-side reflection surface 21. It is preferable that the reflectivity of the light guide plate-side reflection surface 21 is high. Specifically, the reflectivity thereof is preferably 90% or greater and more preferably 95% or greater. From the viewpoint of sufficiently mixing light between the light guide plate-side reflection surface 21 and the reflection surface 12 a of the rear-side reflective plate 12, it is preferable that the depolarization degree of the light guide plate-side reflection surface 21 is high. Specifically, the depolarization degree thereof is preferably 90% or greater. Further, the light guide plate-side reflection surface 21 may reflect light through specular reflection or diffusion reflection. As the material constituting the light guide plate-side reflection surface 21, for example, white polyethylene terephthalate (hereinafter, referred to as white PET) formed by mixing a white pigment into polyethylene terephthalate (PET) is suitable, but the material is not limited thereto.

The emission-side reflection surface 22 of the perforated reflective plate 20 is a reflection surface that reflects light (mainly reflected light that is reflected by the circular polarization reflection film 30) incident from the circular polarization reflection film 30 side, and the depolarization degree thereof is 60% or less. Further, the region that functions as the reflection surface is a region excluding the openings 24 a from the emission-side reflection surface 22. It is preferable that the reflectivity of the emission-side reflection surface is high. Specifically, the reflectivity thereof is preferably 90% or greater and more preferably 95% or greater.

The circular polarization L_(L) reflected by the circular polarization reflection film 30 is incident on the emission-side reflection surface 22, is specularly reflected by this emission-side reflection surface 22 so that the orientation of the polarized light is reversed, and is incident on the circular polarization reflection film 30 again as the circular polarization L_(R) having an orientation of being transmitted through the circular polarization reflection film 30. Even in a case where a part of the retroreflected light is diffusively reflected by the emission-side reflection surface 22 or depolarization occurs, the light can be reused through a plurality of times of reflection. However, since stray light is generated due to the repeated reflection so that the quantity of light which cannot be reused is increased, it is preferable that the emission-side reflection surface 22 is less likely to reflect light through diffusion reflection and the depolarization degree thereof is as small as possible.

In a case where the depolarization degree of the emission-side reflection surface 22 is 60% or less, the effect of improving the luminance can be sufficiently obtained by reusing reflected light through retroreflection. Further, the depolarization degree thereof is more preferably 30% or less and still more preferably 10% or less.

In addition, from the viewpoint that the depolarization degree is small and light can be specularly reflected while the state of polarized light is maintained, it is preferable that the emission-side reflection surface 22 is a specular reflection surface. Further, a small depolarization degree is likely to be obtained in a case where the specular reflection surface is configured of a specular reflective plate formed of a single-layer film compared to a specular reflection surface that is configured of a specular reflective plate formed of a multilayer film obtained by laminating different materials. Among examples of the specular reflective plate formed of a single-layer film, it is preferable that the specular reflection surface is configured of a specular reflective plate formed of a single-layer film obtained by vapor-depositing a metal such as silver, aluminum, or tin. Among the examples, a specular reflective plate obtained by vapor-depositing silver is particularly preferable. Further, a film formed by laminating a plurality of films made of the same material is included in the range of the single-layer film.

The reflectivity and the depolarization degree of the light guide plate-side reflection surface 21 or the emission-side reflection surface 22 of the perforated reflective plate 20 are measured as follows.

—Reflectivity—

A sample to be measured is placed on an automatic absolute reflectivity measuring device M-500V (manufactured by JASCO Corporation), the reflectivity of light incident on the surface (reflection surface) of the sample at an angle of 5° C. with respect to the normal line is measured, and this reflectivity is set as the reflectivity of the reflection surface thereof. In the present specification, the reflectivity of the reflection surface of the perforated reflective plate indicates a reflectivity of the reflection surface that does not have an opening.

—Depolarization Degree—

The luminance is measured by transmitting parallel light through a polarizer having a transmission axis at 0°, allowing the light to pass through a λ/4 plate having a slow axis at 45°, allowing the light to be incident on the surface (reflection surface) of the sample at an angle of 5° with respect to the normal line, allowing this reflected light to pass through the λ/4 plate on the emission side to pass through an analyzer, and disposing a color luminance meter (BM-5 (manufactured by TOPCON Corporation)).

During measurement, the λ/plate on the emission side and the analyzer are allowed to rotate as appropriate, the angles at which a minimum luminance (Ymin) and a maximum luminance (Ymax) are obtained are found, and the depolarization degree is calculated using Equation (1) based on the minimum luminance and the maximum luminance. Depolarization degree=100×(1−(Ymax−Ymin)/(Ymax+Ymin))  Equation (1)

In the present specification, the depolarization degree of the reflection surface of the perforated reflective plate indicates a depolarization degree of the reflection surface which does not have an opening.

The area ratio (the percentage of the total area of the openings 24 a of a plurality of fine holes 24 to the total area of the emission-side reflection surface 22 that includes the opening region) of the openings 24 a of the fine holes 24 to the emission-side reflection surface 22 of the perforated reflective plate 20 is preferably in a range of 10% to 50%. In a case where the area ratio of the openings 24 a is 10% or greater, a decrease in quantity of light to be transmitted from the light guide plate side can be suppressed. Further, in a case where the area ratio thereof is 50% or less, the percentage at which reflected light, which is reflected by the circular polarization reflection film 30 to be incident on the emission-side reflection surface 22, is reflected by the circular polarization reflection film 30 again can be maintained to be a certain value or higher. Therefore, the effect of improving the luminance can be obtained.

The above-described perforated reflective plate 20 can be obtained by vapor-depositing a metal such as silver on one surface of white PET, preparing a double-sided reflective plate which has a metal mirror surface as one surface and white PET as the other surface, and forming through-holes in a predetermined shape such that the double-sided reflective plate have a desired opening ratio. Further, the perforated reflective plate 20 can be also obtained by forming a metal mirror surface on a transparent PET film, adhering the PET film having the metal mirror surface to white PET, preparing a double-sided reflective plate which has a metal mirror surface as one surface and white PET as the other surface, and forming through-holes in the same manner as described above. The thickness of the perforated reflective plate 20 is preferably in a range of 10 to 200 μm.

The through-holes (fine holes) are formed according to a method of forming through-holes using an etching method or a method of forming through-holes using a punch. Moreover, in a case where the number of fine holes is small, the fine holes may be formed by performing laser processing.

(Light Source)

The light source 14 may be a point light source such as a light emitting diode (LED) or a line light source such as rod-like fluorescent light. Further, various known light sources which have been used for edge light type backlight units of the related art can be used as the light source.

(Rear-Side Reflective Plate)

The rear-side reflective plate 12 reflects light propagated through the light guide plate 16 and emitted from the second principal surface 16 c of the light guide plate and reflected light reflected by the circular polarization reflection film 30, transmitted through the fine holes 24 of the perforated reflective plate 20, and incident on the light guide plate 16 again, toward the light guide plate 16. In a case where the backlight unit includes such a rear-side reflective plate 12, the utilization efficiency of light can be improved.

The rear-side reflective plate 12 is not particularly limited and various known reflective plates can be used. In order to efficiently use light, it is preferable that the rear-side reflective plate has a reflection surface that has a low absorption and a high reflectivity. The depolarization degree may be high or low. For example, a reflective plate having a reflection surface formed of a multilayer film obtained by using white PET or a polyester-based resin is suitable, but the plate is not limited thereto. Examples of the multilayer film obtained by using a polyester-based resin include ESR (trade name, manufactured by 3M Japan Limited).

As illustrated in FIG. 1, the rear-side reflective plate 12 may be disposed by being separated from the second principal surface 16 c of the light guide plate 16 or may be bonded to the second principal surface 16 c of the light guide plate 16 using a pressure sensitive adhesive or the like as in a backlight unit 10A illustrated as a design change example 1 in FIG. 3. In a case where the rear-side reflective plate 12 is bonded to the light guide plate 16, the light guiding the light guide plate 16 is repeatedly reflected and guided between the first principal surface 16 b of the light guide plate 16 and the reflection surface 12 a of the rear-side reflective plate 12.

(Circular Polarization Reflection Film)

According to the present embodiment, the circular polarization reflection film 30 is formed of a combination of the λ/4 film 32 and the linearly polarized light reflection film 34 which are disposed in order from the perforated reflective plate 20 side as described above. In FIG. 1, the circular polarization reflection film 30 formed by integrally laminating the λ/4 film 32 and the linearly polarized light reflection film 34 is illustrated, but the circular polarization reflection film 30 may be formed by separating the λ/4 film 32 from the linearly polarized light reflection film 34 and laminating the λ/4 film 32 and the emission-side reflection surface 22 of the perforated reflective plate 20 on each other as in a backlight unit 10B illustrated as a design change example 2 in FIG. 4.

Further, as still another form of a circular polarization reflection film, a circular polarization reflection film 35 may be formed of a combination of a circular polarization separation film 36 and a λ/4 film 38 which are arranged in order from the perforated reflective plate 20 side as in a backlight unit 10C illustrated as a design change example 3 in FIG. 5.

The λ/4 film 32 and the linearly polarized light reflection film 34 that constitute the circular polarization reflection film 30 will be described.

As the linearly polarized light reflection film 34, known films can be appropriately used as long as the film transmits the first linearly polarized light L₁ which is linearly polarized light in a predetermined direction and reflects the second linearly polarized light L₂ which is orthogonal to the first linearly polarized light L₁.

Similarly, the λ/4 film 32 is not particularly limited, and a known λ/4 plate can be used as the film. Further, the λ/4 plate is typically configured of a support and a λ/4 layer formed on the support, but may be configured of only a λ/4 layer obtained by coating a support with a λ/4 layer and then removing the support from the layer. Further, the λ/4 plate may be formed by directly coating the perforated reflective plate 20 or the linearly polarized light reflection film 34 with a λ/4 layer. In a case where the perforated reflective plate 20 or the linearly polarized light reflection film 34 is directly coated with a λ/4 layer, the entire thickness of the backlight unit can be reduced.

The circular polarization separation film 36 and the λ/4 film 38 which constitute the circular polarization reflection film 35 will be described.

Various known films can be used as the circular polarization separation film 36 as long as the film reflects predetermined circular polarization and transmits circular polarization other than the predetermined light.

For example, circular polarization separation plates described in JP1997-133810A (JP-H09-133810A), JP3591699B, and WO2015/029958A can be used. The preferable ranges of the liquid crystal compounds to be used are the same as those described in WO2015/029958A.

Specifically, the circular polarization separation film 36 is formed as follows.

It is preferable that the circular polarization separation film 36 is formed using a liquid crystal material. Further, in a case where the circular polarization separation film 36 is formed using a liquid crystal material, it is preferable that the circular polarization separation film is formed by coating the surface of an alignment film with a coating solution and curing the surface using a support having a surface provided with an alignment film.

In addition, the circular polarization reflection film 35 may be formed by forming an alignment film on a support, forming the λ/4 film 38 on the alignment film, and directly coating the λ/4 film 38 with the circular polarization separation film 36.

As an example, the circular polarization separation film 36 may be formed using a liquid crystal material having a cholesteric structure.

(Cholesteric Structure)

The cholesteric structure is known to exhibit selective reflection properties at a specific wavelength. A central wavelength λ of selective reflection depends on a pitch (period of a helix) of a helical structure in the cholesteric structure and follows a relationship of “λ=n×P” which is the relationship between an average refractive index n and the central wavelength λ. Accordingly, the selective reflection wavelength can be adjusted by adjusting the pitch of this helical structure. Since the pitch of the cholesteric structure depends on the type of a chiral agent used together with a polymerizable liquid crystal compound during the formation of the circular polarization separation film 36 or the addition concentration thereof, a desired pitch can be obtained by adjusting these. Further, the adjustment of the pitch is described in detail in Fujifilm Research Report No. 50 (2005), p. 60 to 63. As a method of measuring the sense or the pitch of a helix, the methods described in “Introduction to Liquid Crystal Chemical Experiment” edited by The Japanese Liquid Crystal Society, published by Sigma Publishing (2007), p. 46 and “Liquid Crystal Handbook”, edited by Liquid Crystal Handbook Editing Committee, Maruzen-Yushodo Company, Ltd., p. 196 can be used.

The cholesteric structure shows a striped pattern formed of bright portions and dark portions in a cross-sectional image showing the circular polarization separation film 36 measured using a scanning electron microscope (SEM). Two repetitions of bright portions and dark portions (two bright portions and two dark portions) correspond to one pitch of a helix. Based on this, the pitch can be measured using a cross-sectional SEM image. Each normal line of the striped pattern is a helical axis direction.

Further, reflected light of the cholesteric structure is circular polarization. In other words, the reflected light of the circular polarization separation film 36 is circular polarization as described above. Whether the reflected light is right circular polarization or left circular polarization depends on the twisted direction of the helix in the cholesteric structure. In the selective reflection caused by the cholesteric liquid crystal, right circular polarization is reflected in a case where the twisted direction of the helix in the cholesteric structure is right and left circular polarization is reflected in a case where the twisted direction of the helix is left. In the example of FIG. 3, left circular polarization is reflected.

As the circular polarization separation film 36, any of a right twisted cholesteric liquid crystal and a left twisted cholesteric liquid crystal may be used. Further, the direction of revolving a cholesteric liquid crystalline phase can be adjusted depending on the type of a liquid crystal compound or the type of a chiral agent to be added.

In a half-width Δλ (nm) of a selective reflection band (circular polarization reflection band) showing the selective reflection, Δλ depends on a pitch P and a birefringence Δn of a liquid crystal compound and follows a relationship of Δλ=Δn×P. Accordingly, the width of the selective reflection band can be controlled by adjusting Δn. Further, Δn can be adjusted by adjusting the type of a polymerizable liquid crystal compound or a mixing ratio thereof or controlling the temperature at the time of alignment fixation.

The half-width of a reflection wavelength range is adjusted depending on the performance or the like required for a backlight unit. The half-width of the reflection wavelength range may be, for example, in a range of 50 to 500 nm and preferably in a range of 100 to 300 nm.

In FIG. 3, the circular polarization separation film 36 is illustrated as one layer. However, the circular polarization separation film 36 may have a multilayer configuration.

For example, the circular polarization separation film 36 that reflects left circular polarization L_(L) and transmits right circular polarization L_(R) may have a configuration of three layers consisting of a layer which corresponds to red light (R light), reflects left circular polarization of L_(L) of red light, and transmits light other than the left circular polarization L_(L) of red light; a layer which corresponds to green light (G light), reflects left circular polarization L_(L) of green light, and transmits light other than the left circular polarization L_(L) of green light; and a layer which corresponds to blue light (B light), reflects left circular polarization L_(L) of blue light, and transmits light other than the left circular polarization L_(L) of blue light.

Alternatively, the circular polarization separation film 36 that reflects left circular polarization L_(L) and transmits right circular polarization L_(R) may have a configuration of two layers consisting of a layer which corresponds to R light and G light, reflects left circular polarization L_(L) of red and green light, and transmits light other than the left circular polarization L_(L) of red and green light; and a layer which corresponds to blue light (B light), reflects left circular polarization L_(L) of blue light, and transmits light other than the left circular polarization L_(L) of blue light.

Alternatively, the circular polarization separation film 36 that reflects left circular polarization L_(L) and transmits right circular polarization L_(R) may have a configuration of two layers consisting of a layer which corresponds to R light, reflects left circular polarization L_(L) of red light, and transmits light other than the left circular polarization L_(L) of red light; and a layer which corresponds to green light and blue light, reflects left circular polarization L_(L) of green and blue light, and transmits light other than the left circular polarization L_(L) of green and blue light.

In the circular polarization separation film 36 having such a multilayer configuration, layers with respective colors may be laminated in any order.

The layers corresponding to respective colors of R light, G light, and B light can be formed by adjusting the helical pitch in the cholesteric structure of the liquid crystal material forming the circular polarization separation film 36. Further, the helical pitch in the cholesteric structure can be adjusted by, for example, selecting the type of chiral agent or the addition concentration of the chiral agent.

The circular polarization separation film 36 having such a multilayer structure can be prepared by applying and curing a liquid crystal composition which becomes the first layer to form the first layer and applying a liquid crystal composition which becomes the second layer onto the first layer and curing the layer to form the second layer, in a case of the two-layer configuration. Further, the third and subsequent layers can be formed according to the same method as described above.

The circular polarization reflection film 35 has a configuration in which the λ/4 film 38 is provided on the light emission side of the circular polarization separation film 36. As described above, the circular polarization reflection film 35 may be a laminated film formed by directly coating the λ/4 film 38 with the circular polarization separation film 36 or a laminated film formed by adhering the circular polarization separation film 36 and the λ/4 film 38, which have been separately prepared, to each other using a pressure sensitive adhesive layer. In a case where the circular polarization separation film 36 and the λ/4 film 38 are disposed in this order from the perforated reflective plate 20 side, the both films 36 and 38 may not be allowed to adhere to each other or may not be brought into contact with each other. As the λ/4 film 38, for example, a known λ/4 plate such as a λ/4 plate obtained by forming an alignment film on a support and forming an optically anisotropic layer that contains a liquid crystal compound on the alignment film or a λ/4 plate obtained by laminating a retardation film can be used.

The right circular polarization L_(R) which has been transmitted through the circular polarization separation film 36 is converted into linearly polarized light corresponding to the backlight-side polarizing plate 39 by the λ/4 film 38 and then emitted from the emission surface side of the λ/4 film 38 (that is, the circular polarization reflection film 35).

Since the backlight unit 10 of the present embodiment described above and the backlight units 10A to 10C of the design change examples 1 to 3 respectively include the perforated reflective plate 20 and the depolarization degree of the emission-side reflection surface 22 is 60% or less, the depolarization of predetermined circular polarization reflected by the circular polarization reflection film 30 or 35 is suppressed, the orientation of the polarized light is reversed by the emission-side reflection surface 22, and a large quantity of reflected light components can be allowed to be incident on the circular polarization reflection film 30 again as the circular polarization having an orientation of being transmitted through the circular polarization reflection film 30. An increase in stray light generated in a case where the reflection of reflected light is repeated several times can be suppressed, reuse of the reflected light can be efficiently performed, and the effect of improving the luminance can be sufficiently obtained.

In a backlight unit of the related art, there is a case where a prism sheet is disposed between a light guide plate and a polarized light reflective plate for the purpose of improving the luminance, but the depolarization degree of polarized light is increased and the utilization efficiency of reflected light is decreased in a case where a prism sheet is used. Meanwhile, the backlight unit of the present invention does not include a prism sheet or a diffusion plate that increases the depolarization degree of polarized light reflected by the reflective polarizer, and thus the depolarization degree of the reflection surface of polarized light is 60% or less, which is small, and the state of polarized light can be maintained. Therefore, polarized light reflected by the circular polarization reflection film can be efficiently used.

FIG. 6 is a schematic cross-sectional view schematically illustrating the configuration of a backlight unit 40 according to the second embodiment. The same elements as in the backlight unit 10 according to the first embodiment illustrated in FIG. 1 are denoted by the same reference numerals and the detailed description thereof will not be provided. The same applies hereinafter.

As illustrated in FIG. 6, the backlight unit 40 of the present embodiment is different from the backlight unit 10 of the first embodiment in terms that a lens sheet 42 is provided on the light guide plate-side reflection surface 21 of the perforated reflective plate 20. The lens sheet 42 is a sheet member having a plurality of lens portions 44 on the surface thereof and is bonded to the light guide plate-side reflection surface 21 such that each lens portion 44 is positioned in the opening 24 b of the fine hole 24 on the light guide plate side in the perforated reflective plate 20. In a case where the opening 24 b has the lens portion 44, the directivity of light, to be incident to the opening 24 b, toward the circular polarization reflection film 30 can be increased and thus the front luminance can be improved.

In FIG. 6, the lens sheet 42 in which one lens portion 44 is provided in one fine hole 24 is illustrated, but a lens sheet formed by two-dimensionally arranging a plurality of lens portions in a larger number than the number of fine holes 24 may be used. The lens sheet 42 may be allowed to adhere to the light guide plate-side reflection surface 21 of the perforated reflective plate 20 through a pressure sensitive adhesive.

<Method of Producing Lens Sheet and Adhesion Method>

The lens sheet 42 is not particularly limited as long as the lens sheet is a film having an optical lens. In FIG. 4, the lens portion 44 has a convex shape, but may have a concave shape in a case where the lens portion has a function of converging light on the emission side of the perforated reflective plate 20. From the viewpoint of excellent productivity of the lens sheet 42, it is preferable that the lens portion 44 has a convex shape. As the lens sheet, for example, a lens film described in JP2015-49363A can be suitably used.

Examples of the shape of the lens portion 44 include a spherical segment shape (shape formed by cutting a sphere out with a plane), a spherical segment stand shape (shape formed by cutting a sphere with two planes in parallel with each other), an ellipsoidal spherical segment shape (shape formed by cutting a revolving ellipsoid out with one plane), an ellipsoidal spherical segment stand shape (shape formed by cutting a revolving ellipsoid out with two planes in parallel with each other), a pyramid shape, a truncated pyramid shape, a conical shape, a truncated cone shape, a Fresnel shape, a diffraction lattice shape, a prism shape, and a cylindrical shape. These shapes of the lens portions 44 may be used alone or in combination of two or more kinds thereof. Among the shapes of the lens portions 44, from the viewpoint of excellent luminance, a spherical segment shape, a spherical segment stand shape, an ellipsoidal spherical segment shape, an ellipsoidal spherical segment stand shape, a pyramid shape, a truncated pyramid shape, a conical shape, and a truncated cone shape are preferable; and a spherical segment shape, an ellipsoidal spherical segment shape, a pyramid shape, and a truncated pyramid shape are more preferable.

In a case where the shape of the lens portion 44 is a spherical segment shape, a spherical segment stand shape, an ellipsoidal spherical segment shape, an ellipsoidal spherical segment stand shape, a pyramid shape, a truncated pyramid shape, a conical shape, or a truncated cone shape, the aspect ratio of the lens portion 44 is preferably in a range of 0.3 to 1.4, more preferably in a range of 0.35 to 1.3, and still more preferably in a range of 0.4 to 1.0 from the viewpoint of excellent luminance. Further, the aspect ratio of the lens portion 44 is set as a ratio of the height of the lens portion 44 to the longest diameter of the bottom portion of the lens portion 44.

From the viewpoint of excellent luminance, the height of the lens portion 44 is preferably in a range of 0.25 to 75 μm, more preferably in a range of 0.5 to 65 μm, and still more preferably in a range of 1 to 50 μm.

In the present specification, the height of the lens portion 44 indicates the height from the flat surface of the sheet on which the lens portion 44 is provided to the highest portion (vertex) of the lens portion 44 in a case of the convex structure. Further, the height thereof indicates the depth from the flat surface of the sheet on which the lens portion 44 is provided to the lowest portion in a case of the concave structure. In addition, the height of the lens portion 44 is obtained by imaging the cross section of the lens sheet 42 using a scanning electron microscope, measuring the height of each lens portion 44 at five sites, and acquiring the average value thereof.

From the viewpoint of excellent luminance, the pitch of the lens portions 44 is preferably in a range of 0.5 to 150 μm, more preferably in a range of 1 to 130 μm, and still more preferably in a range of 2 to 100 μm.

In the present specification, the pitch of the lens portions 44 indicates the shortest distance between the highest portions or the lowest portions of the lens portions 44. The pitch of the lens portions 44 is obtained by imaging the surface of the lens sheet 42 having the lens portions 44 using a scanning electron microscope, measuring the shortest distance between the highest portions or the lowest portions of the lens portions 44 at five sites, and acquiring the average value thereof.

Examples of the shapes of the bottom portions (portions on the flat surface) of the lens portions 44 include a quadrangle such as a square or a rectangle; a circle; and an ellipse. The shapes of the bottom portions of the lens portions 44 may be used alone or in combination of two or more kinds thereof. Among the shapes of the bottom portions of the lens portions 44, from the viewpoint of excellent luminance, a quadrangle, a circle, and an ellipse are preferable; and a square, a rectangle, and a circle are more preferable.

In the present specification, the bottom portion of the lens portion 44 indicates a virtual planar portion enclosed by the outer peripheral edge on the flat surface of the sheet on which the lens portion 44 is formed.

The resin in the material of the lens sheet 42 is not particularly limited as long as the resin has cleared a solvent resistance test and has a high light transmittance in a visible light wavelength range (approximately 400 to 700 nm), and examples thereof include an acrylic resin; a polycarbonate resin; a polyester resin such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate; a styrene resin such as polystyrene or an acrylonitrile-butadiene-styrene copolymer (ABS) resin; and a vinyl chloride resin. Among these resins, from the viewpoints of a high light transmittance in a visible light wavelength range and excellent solvent resistance, heat resistance, mechanical characteristics, and forming processability, an acrylic resin is preferable.

From the viewpoint of excellent luminance, the refractive index of the resin in the material of the lens sheet 42 is preferably in a range of 1.40 to 2.00, more preferably in a range of 1.43 to 1.95, and still more preferably in a range of 1.46 to 1.90.

From the viewpoints of excellent light-transmitting properties of the lens sheet 42 and excellent luminance, the content of the resin in the material of the lens sheet 42 is preferably 90% by mass or greater, more preferably 95% by mass or greater, still more preferably 97% by mass or greater, and particularly preferably 99% by mass or greater.

The material of the lens sheet 42 may contain components other than the resin within the range not damaging the performance of the lens sheet 42. Examples of the other components include light diffusing fine particles, a release agent, a flame retardant, an antistatic agent, a leveling agent, an antifouling property improving agent, a dispersion stabilizer, and a viscosity-adjusting agent.

From the viewpoint of suppressing degradation of the performance of the lens sheet 42, the content of other components in the material of the lens sheet 42 is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass, and particularly preferably 1% by mass or less.

As a method of producing the lens sheet 42, a production method of supplying an active energy ray curable composition to a region between a base material and a mold formed by arranging a plurality of transfer portions having a reversed structure of the lens portion 44 and irradiating the region between the mold and the base material with active energy rays may be exemplified.

Examples of a light emitting source of active energy rays include a chemical lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, an electrodeless ultraviolet lamp, a visible light halogen lamp, and a xenon lamp.

The integrated light quantity of the active energy rays may be appropriately set according to the type of the active energy ray curable composition, but is preferably in a range of 0.01 to 10 J/cm² and more preferably in a range of 0.5 to 8 J/cm² from the viewpoints of excellent curability of the active energy ray curable composition and suppressing degradation of the lens sheet 42.

FIG. 7 is a schematic cross-sectional view schematically illustrating the configuration of a backlight unit 50 according to a third embodiment.

The backlight unit 50 of the present embodiment is different from the backlight unit 10 of the first embodiment illustrated in FIG. 1 in terms that a wavelength conversion layer 52 which is excited by the incidence ray and generates light having a wavelength different from the wavelength of the incidence ray is provided on the second principal surface 16 c of the light guide plate 16. Further, the backlight unit 50 is different from the backlight unit 10 of the first embodiment illustrated in FIG. 1 in terms that a light source 15 that emits the incidence ray having an excitation wavelength of the wavelength conversion layer 52 is provided. Except for these points, the backlight unit 50 is the same as the backlight unit 10 and exerts the same effects as those of the backlight unit 10.

The wavelength conversion layer 52 may be directly formed on the second principal surface 16 c of the light guide plate 16, but may be separately prepared to have a sheet shape and then allowed to adhere onto the second principal surface 16 c through a pressure sensitive adhesive. Further, the wavelength conversion layer 52 is not limited to the form provided on the second principal surface 16 c of the light guide plate 16 and may be disposed at a site through which light emitted from the light source 15 passes. For example, the wavelength conversion layer 52 may be provided on the first principal surface 16 b side of the light guide plate 16.

The wavelength conversion layer 52 converts the wavelength of the incidence ray into a relatively long wavelength. The wavelength conversion layer 52 contains a wavelength conversion material 54 which is excited by the incidence ray of a fluorescent body, a quantum dot, or a combination of these and generates light having a wavelength different from that of the incidence ray.

The fluorescent body may typically be an organic fluorescent body or an inorganic fluorescent body. According to an exemplary embodiment, the fluorescent body may be a yellow fluorescent body. Such a yellow fluorescent body may be a YAG-based fluorescent material, a silicate-based fluorescent material, an oxynitride fluorescent material, or a combination of these, but is not limited to these.

The quantum dot has a size of several nanometers to several tens of nanometers as a semiconductor nanoparticle having a core-shell structure and has a characteristic of emitting light having different wavelengths according to the size of particle due to the quantum confinement effect. More specifically, the quantum dot generates intense light in a narrow wavelength band, and light diverging from the quantum dot is generated at the time of transition of an electron in an excited state to a valence band from a conduction band. At this time, the quantum dot has a property in which light having a short wavelength is generated as the particle of the quantum dot is as small as possible and light having a long wavelength is generated as the particle thereof. Accordingly, by adjusting the size of the quantum dot, entire light in a visible light range having a desired wavelength can be emitted.

The quantum dot may contain any one nanocrystal from among a Si-based nanocrystal, a Group II-VI compound semiconductor nanocrystal, a Group III-V compound semiconductor nanocrystal, a Group IV-VI compound semiconductor nanocrystal, and a mixture of these.

The Group II-VI compound semiconductor nanocrystal may be any one of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HggZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe.

Further, the Group III-V compound semiconductor nanocrystal may be any one of GaPAs, AlNP, AINAs, AlPAs, InNP, InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP, InAlNAs, and InAlPAs; and the Group IV-VI compound semiconductor nanocrystal may be SbTe.

The wavelength conversion layer 52 may contain one kind of quantum dots. For example, the wavelength conversion layer 52 may contain yellow quantum dots converting the wavelength of the incidence ray into a wavelength of yellow light. However, the kind of quantum dots to be contained therein is not limited thereto, and the wavelength conversion layer 52 may contain two or more kinds of quantum dots. For example, the wavelength conversion layer 52 may contain red quantum dots converting the wavelength of the incidence ray into a wavelength of red light and green quantum dots converting the wavelength of the incidence ray into a wavelength of green light.

The wavelength conversion layer 52 may further contain a dispersion medium that disperses wavelength conversion materials other than the wavelength conversion material 54 such as a fluorescent body or quantum dots. In other words, the fluorescent body or quantum dots can be dispersed in the form of being naturally coordinated to a dispersion medium such as an organic solvent or a polymer resin. As such a dispersion medium, any medium can be used as long as the medium is transparent within the range not impacting the wavelength conversion performance of the fluorescent body or quantum dots, not reflecting light, and not causing light absorption.

The organic solvent may contain at least one of toluene, chloroform, or ethanol, and the polymer resin may contain at least one of epoxy, silicone, polystyrene, or acrylate.

Further, the wavelength conversion layer 52 may further contain a UV initiator, a thermosetting additive, a crosslinking agent, a diffusing agent, and a combination of these other than the dispersion medium.

The backlight unit 50 of the present embodiment may include a blue LED as the light source 15 and a wavelength conversion layer 52 formed by dispersing quantum dots which are excited by blue light and emit green light and quantum dots which are excited by blue light and emit red light in a matrix.

In addition, the wavelength conversion layer 52 may be interposed between two sheets of barrier films that suppress transmission of oxygen and moisture.

Hereinbefore, the backlight unit of the present invention has been described in detail, but the present invention is not limited to the above-described examples, and various improvements or modifications can also be made within the range not departing from the scope of the present invention.

EXAMPLES

Hereinafter, the present invention will be described in more detail with reference to examples. The materials, the reagents, the use amounts, the amounts of materials, the ratios, the treatment contents, and the treatment procedures shown in the examples described below can be changed as appropriate within the range not departing from the gist of the present invention. Therefore, the scope of the present invention should not be limitatively interpreted by the following specific examples.

Example 1

A preparation method of Example 1 will be described.

First, a rear-side reflective plate was obtained by adhering white polyethylene terephthalate (hereinafter, white PET) formed by mixing a white pigment into polyethylene terephthalate (PET) having a thickness of 100 μm to an acrylic plate having a thickness of 2 mm. The white PET surface constitutes the reflection surface.

An acrylic plate having a thickness of 2 mm was used as a light guide plate. A perforated reflective plate E-1A described below was disposed on one principal surface of the light guide plate and the above-described rear-side reflective plate was disposed on the other principal surface facing the one principal surface thereof. In addition, a circular polarization reflection film 1 described below was disposed on the opposite side of the light guide plate of the perforated reflective plate E-1A. The interval between the light guide plate and the rear-side reflective plate was set to 50 μm A light source of a white LED was disposed at a position where the emitted light from the light source was incident on an end surface of the light guide plate.

In this manner, an edge light type backlight unit was prepared.

—Perforated Reflective Plate E-1A—

An iPad Air (registered trademark) (manufactured by Apple Inc.) was disassembled and a multilayer film used as a reflection film of a backlight was taken out.

A silver reflection film 1 was prepared by forming a silver thin film layer having a thickness of 80 nm on one surface of a PET film having a thickness of 25 μm as a metal reflection layer according to a vacuum deposition method.

The silver reflection film 1 was allowed to adhere to one surface of the multilayer film such that the PET film side became the multilayer film side using a pressure sensitive adhesive (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.). In this manner, a double-sided reflective plate provided with one reflection surface serving as a mirror surface formed of a silver thin film layer and having a small depolarization degree and the other surface serving as a reflection surface formed of a multilayer film and having a large diffusion and a large depolarization degree was obtained.

A plurality of through-holes (fine holes) were formed in this double-sided reflective plate using a hollow punch having a diameter of 1 mm. The plurality of fine holes were formed by adjusting the number of the fine holes such that the opening ratio thereof was set to 10%.

The perforated reflective plate E-1A prepared in the above-described manner was disposed such that the surface of the silver thin film layer was set as a viewing side and the surface of the multilayer film was set as a light guide plate side. Further, the reflectivity of the surface of the silver thin film layer in the silver reflection film 1 was 99% and the depolarization degree was 4%. Further, the reflectivity of the surface of the multilayer film was 99% and the depolarization degree was 95%. The reflectivity and the depolarization degree of both surfaces were measured in the state before the fine holes were formed. The reflectivity and the depolarization degree were measured according to the above-described measuring method. The same applies to the following examples.

—Circular Polarization Reflection Film 1—

The circular polarization reflection film 1 was formed of a λ/4 film and a linearly polarized light reflection film. Both films were allowed to adhere to each other using a pressure sensitive adhesive such that the angle between the transmission axis of the linearly polarized light reflection film and the slow axis of the λ/4 film was set to 45°, thereby preparing a circular polarization reflection film 1.

Here, a QL film (manufactured by Fujifilm Corporation) was used as the λ/4 film. As the linearly polarized light reflection film, an iPad Air (registered trademark) (manufactured by Apple Inc.) was disassembled and a film used as a luminance improvement film was taken out and then used.

The circular polarization reflection film 1 was disposed such that the λ/4 film was on the perforated reflective plate side.

Example 2

A perforated reflective plate P-2A was used in place of the perforated reflective plate E-1A of Example 1. A backlight unit of Example 2 was prepared in the same manner as in Example 1 except that the perforated reflective plate P-2A was used.

—Perforated Reflective Plate P-2A—

White PET having a thickness of 100 μm similar to that of the rear-side reflective plate was prepared. Further, a silver reflection film 2 was obtained by coating one surface of a PET film having a thickness of 25 μm with a mixture formed by mixing 4% by mass of transparent fine particles, having a particle diameter of 6 μm and being formed of an urethane-based resin, into a polyester urethane-based resin according to a gravure coating method, preparing an uneven layer on the surface thereof, and forming a silver thin film layer having a thickness of 80 nm as a metal reflection layer according to a vacuum deposition method.

The silver reflection film 2 was allowed to adhere to one surface of the white PET such that the PET film side became one surface side of the white PET using a pressure sensitive adhesive (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.). In this manner, a double-sided reflective plate provided with one surface serving as a mirror surface formed of a silver thin film layer and having a small depolarization degree and the other surface serving as a reflection surface formed of white PET and having a large diffusion and a large depolarization degree was obtained.

A plurality of through-holes (fine holes) were formed in this double-sided reflective plate using a hollow punch having a diameter of 1 mm. The plurality of fine holes were formed by adjusting the number of the fine holes such that the opening ratio thereof was set to 10%.

The perforated reflective plate P-2A prepared in the above-described manner was disposed such that the surface of the silver thin film layer was set as a viewing side and the surface of the white PET was set as a light source side. Further, the reflectivity of the surface of the silver thin film layer in the silver reflection film 2 was 99% and the depolarization degree was 30%. Further, the reflectivity of the surface of the white PET was 99% and the depolarization degree was 95%.

Example 3

A perforated reflective plate P-3A was used in place of the perforated reflective plate P-2A of Example 2. A backlight unit of Example 3 was prepared in the same manner as in Example 2 except that the perforated reflective plate P-3A was used.

—Perforated Reflective Plate P-3A—

The perforated reflective plate P-3A was prepared in the same manner as that for the perforated reflective plate P-2A except that a silver reflection film 3 was used in place of the silver reflection film 2.

The silver reflection film 3 was obtained by coating one surface of a PET film having a thickness of 25 μm with a mixture formed by mixing 15% by mass of transparent fine particles, having a particle diameter of 6 μm and being formed of an urethane-based resin, into a polyester urethane-based resin according to a gravure coating method, preparing an uneven layer on the surface thereof, and forming a silver thin film layer having a thickness of 80 nm as a metal reflection layer according to a vacuum deposition method. Further, the reflectivity of the surface of the silver thin film layer in the silver reflection film 3 was 99% and the depolarization degree was 60%.

Example 4

A perforated reflective plate P-1B was used in place of the perforated reflective plate P-2A of Example 2. A backlight unit of Example 4 was prepared in the same manner as in Example 2 except that the perforated reflective plate P-1B was used.

—Perforated Reflective Plate P-1B—

The silver reflection film 1 was used in place of the silver reflection film 2 in the perforated reflective plate P-2A. Further, the opening ratio of fine holes was adjusted to 25% at the time of forming the fine holes. A perforated reflective plate P-1B was obtained in the same manner as that for the perforated reflective plate P-2A except for these points.

Example 5

A perforated reflective plate P-2B provided with fine holes having an opening ratio of 25% was used in the same configuration of the perforated reflective plate 2A of Example 2. A backlight unit of Example 5 was prepared in the same manner as in Example 2 except that the perforated reflective plate P-2B was used.

Example 6

A perforated reflective plate P-1C provided with fine holes having an opening ratio of 50% was used in the same configuration of the perforated reflective plate P-1B of Example 4. A backlight unit of Example 6 was prepared in the same manner as in Example 4 except that the perforated reflective plate P-1C was used.

Example 7

A circular polarization reflection film 2 was used in place of the circular polarization reflection film 1 in Example 1. A backlight unit of Example 7 was prepared in the same manner as in Example 1 except that the circular polarization reflection film 2 was used.

The circular polarization reflection film 2 includes a λ/4 layer formed by being applied onto the silver reflection film 1 of the perforated reflective plate E-1A in place of a QL film (manufactured by Fujifilm Corporation) as a λ/4 film.

—Formation of λ/4 Film on Silver Reflection Film—

A λ/4 was formed on the silver reflection film 1 before holes were formed in the step of preparing the perforated reflective plate E-1A. After the surface of the silver reflection film 1 was subjected to a surface treatment, an alignment layer was formed and a λ/4 layer was formed on the alignment layer.

<Formation of Alignment Layer>

The surface of the silver reflection film was subjected to a surface treatment by performing a corona treatment and then continuously coated with an alignment layer coating solution having the following composition using a #14 wire bar.

(Alignment Layer Coating Solution)

Modified polyvinyl alcohol described below   10 parts by mass Water  371 parts by mass Methanol  119 parts by mass Glutaraldehyde  0.5 parts by mass Photopolymerization initiator (IRGACURE  0.3 parts by mass (registered trademark) 2959) (In the following structural formula, the proportion is a molar ratio.)

Modified Polyvinyl Alcohol

The applied alignment layer coating solution was dried by hot air at 60° C. for 60 seconds and further dried by hot air at 100° C. for 120 seconds.

A rubbing treatment was continuously performed on the obtained coated film, thereby preparing a support provided with an alignment layer. Further, the rubbing treatment was performed such that the longitudinal direction of the support was in parallel with the transport direction and a rotation axis of a rubbing roller was set in a direction of 45° clockwise with respect to the longitudinal direction of the support.

<Formation of λ/4 Layer>

A coating solution for forming a λ/4 layer described below was prepared.

(Coating Solution for Forming λ/4 Layer)

Discotic liquid crystal compound (the following D1)   80 parts by mass Discotic liquid crystal compound (the following D2)   20 parts by mass Alignment assistant agent (the following OA1)  0.9 parts by mass Alignment assistant agent (the following OA2)  0.1 parts by mass Polymerization initiator (the following IN2)    3 parts by mass Methyl ethyl ketone (MEK)  301 parts by mass

The alignment layer was continuously coated with the coating solution for forming a λ/4 layer using a #3.6 wire bar. The transport speed of the support was 20 m/min.

For the purpose of drying the solvent of the coating solution and alignment maturing of the discotic liquid crystal compound, the support was heated with hot air at 60° C. for 90 seconds. Next, ultraviolet ray emission (200 mJ/cm²) was performed at 70° C., and the alignment of the liquid crystal compound was fixed to form a λ/4 layer.

In this manner, the alignment layer and the λ/4 layer were formed on the silver reflection film 1 of the double-sided reflective plate formed by adhering the silver reflection film 1 onto a multilayer film, and holes were formed in the same manner as in Example 1, thereby obtaining a perforated reflective plate 1-EA provided with a λ/4 layer.

Example 8

An iPad Air (registered trademark) (manufactured by Apple Inc.) was disassembled and a multilayer film used as a reflection film of a backlight was taken out and then used as a rear-side reflective plate. A backlight unit of Example 8 was prepared in the same manner as in Example 1 except that this multilayer film was used as a rear-side reflective plate was used in place of the white PET and the multilayer film and the light guide plate were allowed to adhere to each other using a pressure sensitive adhesive (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.).

Example 9

A backlight unit of Example 9 was prepared in the same manner as in Example 1 except that a lens sheet was attached to the surface of the perforated reflective plate E-1A on the multilayer film side.

Further, in the procedures for preparing the perforated reflective plate E-1A, a pressure sensitive adhesive (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) was allowed to adhere to the surface on the multilayer film side before fine holes were formed so that holes were also formed in the pressure sensitive adhesive layer at the same time with the formation of the fine holes.

A lens sheet was prepared using an acrylic resin with reference to the method described in JP2015-49363A. The formed pitch of a lens in the lens sheet was 10 μm, and the lens shape was circular in a plan view. As the base material of the lens sheet, an acrylic sheet having a thickness of 2 mm was used.

The lens sheet was allowed to adhere to the surface of the perforated reflective plate 1A on the multilayer film side such that the lens surface side was brought into close contact with the pressure sensitive adhesive layer. Since the uneven lens was filled with the pressure sensitive adhesive in the portion other than the fine holes, the condensing effect of the lens appeared only in the holes.

Example 10

A thick perforated reflective plate P-1AT including a PET laminate was used in place of the perforated reflective plate E-1A in Example 1. A backlight unit of Example 10 was prepared in the same manner as in Example 1 except that the perforated reflective plate P-1AT was used.

—Perforated Reflective Plate P-1AT—

Four sheets of white PET having a thickness of 100 μm formed by using a rear-side reflective plate were laminated using a pressure sensitive adhesive having a thickness of 25 μm (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.), thereby obtaining a PET laminate having a thickness of 475 μm. The silver reflection film 1 was allowed to adhere to one surface of the PET laminate using the same pressure sensitive adhesive, and holes were formed in the same manner as in Example 1 using a hollow punch having a diameter of 100 μm, thereby obtaining a perforated reflective plate P-1AT.

The perforated reflective plate 1D of the present example had a thickness t of 500 μm, the fine holes had an opening diameter d of 100 μm, and the thickness t and the opening diameter d satisfied an equation of “t/d=5”.

Example 11

A circular polarization reflection film 3 was used in place of the circular polarization reflection film 1 in Example 1. A backlight unit of Example 11 was prepared in the same manner as in Example 1 except that the circular polarization reflection film 2 was used.

—Circular Polarization Reflection Film 3—

The circular polarization reflection film 3 was configured to be formed of a λ/4 film (λ/4 layer) and a cholesteric liquid crystal layer functioning as a circular polarization separation film.

—Preparation of Circular Polarization Reflection Film 3—

<<Preparation of Support Provided with Alignment Layer>>

<<Alkali Saponification Treatment of Cellulose Acylate Film Base Material>>

A long cellulose acylate film (TD40UL, manufactured by Fujifilm Corporation) was used as a support.

The support was allowed to pass through a dielectric heating roll at a temperature of 60° C. and the surface temperature of the film was increased to 40° C. Thereafter, one surface of the support was coated with an alkali solution having the following composition such that the coating amount thereof was set to 14 ml/m² using a bar coater, and then the surface was heated to 110° C.

(Alkali Solution)

Potassium hydroxide  4.7 parts by mass Water 15.8 parts by mass Isopropanol 63.7 parts by mass Surfactant (C₁₄H₂₉O(CH₂CH₂O)₂₀H)   1 part by mass Propylene glycol 14.8 parts by mass

The support coated with the alkali solution was transported for 10 seconds under a steam type far infrared heater (manufactured by NORITAKE CO., LTD.).

Next, the support was coated with pure water in a ratio of 3 ml/m² using a bar coater. Next, the support was washed with water using a fountain coater and dewatered using an air knife three times, transported to a drying zone at 70° C. for 10 seconds, and dried, thereby preparing a support (cellulose acylate film) having a surface subjected to an alkali saponification treatment.

<<Formation of Alignment Layer>>

An alignment layer coating solution was prepared according to the same method as the method of forming the alignment layer described in Example 7, and the surface of the support, on which the alkali saponification treatment had been performed, was coated with the alignment layer coating solution so that an alignment layer was formed, thereby preparing a support provided with an alignment layer.

<Preparation of Support Provided with λ/4 Layer>

A coating solution for forming a λ/4 layer was prepared according to the same method as the method of forming the λ/4 layer described in Example 7, a λ/4 layer was applied to and formed on the alignment layer, thereby preparing a support provided with a λ/4 layer.

<Preparation of Circular Polarization Separation Plate>

A coating solution (D-IV) containing the following discotic liquid crystal compound was prepared.

(Coating solution (D-IV) containing discotic liquid   80 parts by mass crystal compound) Discotic liquid crystal compound (D1 described above) Discotic liquid crystal compound (D2 described   20 parts by mass above) Chiral agent (the following CH4)  3.8 parts by mass Polymerization initiator (IRGACURE (registered    3 parts by mass trademark) 2959) Polymerization initiator (the following IN4)    1 part by mass Methyl ethyl ketone (MEK) 189.9 parts by mass tert-Butyl alcohol  58.4 parts by mass Cyclohexane  43.8 parts by mass

The λ/4 layer of the prepared support provided with a λ/4 layer was continuously coated with the coating solution (D-IV) containing a discotic liquid crystal compound using a #3.6 wire bar. The transport speed of the film was 20 m/min.

For the purpose of drying the solvent of the coating solution and alignment maturing of the discotic liquid crystal compound, the film was heated with hot air at 110° C. for 160 seconds. Next, ultraviolet ray emission (150 mJ/cm²) was performed at 50° C. and the alignment of the liquid crystal compound was fixed, thereby preparing a first layer of a circular polarization separation film having a film thickness of 3 μm.

<<Preparation of Optical Laminate (A)>>

First, a terminal fluorinated alkyl group-containing polymer (compound A) having an optically active site was obtained by performing the procedures described in paragraph [0065] of JP4570377B. Specifically, a compound A was obtained as follows.

50 parts by mass of a fluorine-based solvent AK-225 (manufactured by ASAHI GLASS CO., LTD., a mixed solvent of 1,1,1,2,2-pentafluoro-3,3-dichloropropane and 1,1,2,2,3-pentafluoro-1,3-dichloropropane at a molar ratio of 1:1.35) and 5.22 parts by mass of a reactive chiral agent (a compound 7, the symbol “*” in the formula represents an optically active site) having optical activity with the following structure were put into a four-neck flask provided with a condenser, a thermometer, a stirrer, and a dropping funnel, the temperature of the reaction container was adjusted to 45° C., and 6.58 parts by mass of a 10 mass % solution of diperfluoro-2-methyl-3-oxahexanoyl peroxide/AK225 was added dropwise to the reaction container. After completion of the dropwise addition, the solution was allowed to react in a nitrogen stream at 45° C. for 5 hours, and the product was concentrated to 5 ml, re-precipitated with hexane, and dried, thereby obtaining 3.5 parts by mass (yield of 60%) of a terminal fluorinated alkyl group-containing polymer (compound A) having an optically active site.

The molecular weight of the obtained polymer was measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a developing solvent. As the result, Mn was 4,000 (Mw/Mn=1.77). Further, the fluorine content was measured, and the fluorine content was 5.89% by mass.

One surface of a long cellulose acylate film (TD80UL (manufactured by Fujifilm Corporation) having a size of 100 meters or greater was coated with an alignment film coating solution containing 10 parts by mass of polyvinyl alcohol and 371 parts by mass of water and dried, thereby forming an alignment film having a thickness of 1 μm. Next, a rubbing treatment was continuously performed on the alignment film in a direction parallel to the longitudinal direction of the film.

The alignment film was coated with a composition for forming a cholesteric liquid crystal layer (A) with the following composition using a bar coater, dried at room temperature for 10 seconds, heated (alignment maturing) in an oven at 100° C. for 2 minutes, and irradiated with ultraviolet rays for 30 minutes, thereby preparing an optical laminate (A) having a cholesteric liquid crystal layer (A) with a thickness of 5 μm.

(Composition for Forming Cholesteric Liquid Crystal Layer (A))

The following compound 8 8.2 parts by mass Polymerization initiator (IN2 described above) 0.3 parts by mass Terminal fluorinated alkyl group-containing 1.9 parts by mass polymer (compound A) having optically active site prepared as described above Methyl ethyl ketone  24 parts by mass

As the result of observation of a cross section of the cholesteric liquid crystal layer (A) using a scanning electron microscope, it was found that the layer had a helical axis in the layer normal direction and a structure in which the cholesteric pitch was continuously changed. Here, in regard to the cholesteric pitch, at the time of observation of the cross section of the cholesteric liquid crystal layer using a scanning electron microscope, the width of the layer formed by a bright part and a dark part being repeated two times (bright-dark-bright-dark) in the layer normal direction was counted as one pitch.

Further, in a case where the short wavelength side of the cholesteric pitch in the short thickness direction is defined as an x surface and the long wavelength side thereof is defined as a y surface, as the result of measurement of the cholesteric pitch using AXOSCAN (manufactured by Axometrics, Inc.), the cholesteric reflection wavelength in the vicinity of the x surface side was 500 nm and the cholesteric reflection wavelength in the vicinity of the y surface side was 700 nm.

From the viewpoints of manufacturing suitability and enabling preparation of an optical sheet member using a so-called roll-to-roll system, it is preferable to use a long cellulose acylate film. The long film to be used is not limited thereto as long as the cholesteric liquid crystal layer can be transferred.

The first layer of the circular polarization separation film prepared in the above-described manner and the optical laminate (A) were bonded by allowing the first layer and the cholesteric liquid crystal layer (A) to face each other using an acrylic UV curing adhesive according to a roll-to-roll system. Next, the cellulose acylate film was peeled off from the optical laminate (A) and only the cholesteric liquid crystal layer (A) was transferred onto the first layer to form a second layer of the circular polarization separation film. In this manner, a circular polarization reflection film 3 having a λ/4 layer and a cholesteric layer on the support was obtained.

The circular polarization reflection film 3 was disposed such that the cholesteric liquid crystal layer was positioned on the perforated reflective plate side.

Comparative Example 1

A perforated reflective plate E-A formed of only white PET which was obtained by removing the silver reflection film 1 from the perforated reflective plate E-1A in Example 1 was used. The reflectivities of both surfaces of the perforated reflective plate E-A were respectively 99% and the depolarization degrees thereof were respectively 95%. The perforated reflective plate E-A was used and a configuration free from the circular polarization reflection film and the light guide plate in Example 1 was employed. The same multilayer film as in Example 8 was used as the rear-side reflective plate.

The perforated reflective plate E-A was disposed such that a spacer was interposed between the multilayer film serving as a rear-side reflective plate and the perforated reflective plate E-A such that the interval therebetween was 10 mm. Further, a white LED was disposed at a position of allowing light to be incident to the interval between the perforated reflective plate E-1A and the rear-side reflective plate from a side.

In this manner, an edge light type backlight unit of Comparative Example 1 was prepared.

Comparative Example 2

A light guide plate formed of the same acrylic plate having a thickness of 2 mm as that in Example 1 was disposed between the perforated reflective plate E-1A and the rear-side reflective plate in the backlight unit of Comparative Example 1, and the interval between the perforated reflective plate E-1A and the rear-side reflective plate was set in the same manner as in Example 1.

Comparative Example 3

A backlight unit of Comparative Example 3 was prepared in the same manner as in Comparative Example 2 except that the linearly polarized light reflection film was disposed on the emission surface side (opposite side to the light guide plate) of the perforated reflective plate E-A in the backlight unit of Comparative Example 2. As the linearly polarized light reflection film, similar to the film used in the circular polarization reflection film 1, an iPad Air (registered trademark) (manufactured by Apple Inc.) was disassembled and a film used as a luminance improvement film was taken out and then used.

Comparative Example 4

A perforated reflective plate P-4A was used in place of the perforated reflective plate P-2A in Example 2. A backlight unit of Comparative Example 4 was prepared in the same manner as in Example 2 except that the perforated reflective plate P-4A was used.

—Perforated Reflective Plate P-4A—

The perforated reflective plate P-4A was prepared in the same manner as that for the perforated reflective plate P-2A except that a silver reflection film 4was used in place of the silver reflection film 2.

The silver reflection film 4was obtained by coating one surface of a PET film having a thickness of 25 μm with a mixture formed by mixing 20% by mass of transparent fine particles, having a particle diameter of 6 μm and being formed of an urethane-based resin, into a polyester urethane-based resin according to a gravure coating method, preparing an uneven layer on the surface thereof, and forming a silver thin film layer having a thickness of 80 nm as a metal reflection layer according to a vacuum deposition method. Further, the reflectivity of the surface of the silver thin film layer in the silver reflection film 4was 99% and the depolarization degree was 70%.

Example 12

In the backlight unit of Example 1, a wavelength conversion member was provided on the surface of the light guide plate on the rear-side reflective plate side. Further, a blue LED was used in place of the white LED as a light source. A backlight unit of Example 12 was prepared in the same manner as in Example 1 except for these points. In the present example, the light guide plate and the wavelength conversion member were respectively allowed to adhere to the rear-side reflective plate and the wavelength conversion layer using a pressure sensitive adhesive (SK-DYNE (registered trademark) 2057, manufactured by Soken Chemical & Engineering Co., Ltd.).

—Wavelength Conversion Member—

The wavelength conversion member has a configuration in which a wavelength conversion layer is interposed between two barrier films.

The wavelength conversion member was prepared as follows.

<Preparation of Barrier Film>

An organic layer and an inorganic layer were sequentially formed on one surface side of a support by performing the following procedures using a polyethylene terephthalate film (PET film, trade name: COSMOSHINE (registered trademark), manufactured by TOYOBO Co., LTD., A4300, thickness of 50 μm) as a support.

Trimethylolpropane triacrylate (TMPTA, manufactured by Daicel-Cytec Co., Ltd.) and aphotopolymerization initiator (ESACURE KT046, manufactured by Lamberti S.P.A.) were prepared, weighed such that the mass ratio between these was set to 95:5, and dissolved in methyl ethyl ketone to obtain a coating solution having a concentration of solid contents of 15% by mass. The above-described PET film was coated with this coating solution using a die coater according to a roll-to-roll system and was allowed to pass through a drying zone at an ambient temperature of 50° C. for 3 minutes. Thereafter, the film was irradiated (integrated irradiation quantity of approximately 600 mJ/cm²) with ultraviolet rays in a nitrogen atmosphere, cured by ultraviolet curing, and wound up. The thickness of a first organic layer formed on the support was 1 μm.

Next, an inorganic layer (silicon nitride layer) was formed on a surface of the first organic layer using a chemical vapor deposition (CVD) device having a roll-to-roll system. Silane gas (flow rate of 160 sccm), ammonia gas (flow rate of 370 sccm), hydrogen gas (flow rate of 590 sccm), and nitrogen gas (flow rate of 240 sccm) were used as raw material gas. A high-frequency power source having a frequency of 13.56 MHz was used as a power source. The film forming pressure was 40 Pa and the ultimate thickness was 50 nm.

A laminated film obtained by laminating an inorganic layer on a surface of the first organic layer formed on the support was prepared in the above-described manner.

Further, a second organic layer was formed on a surface of the inorganic layer of the laminated film prepared in the above-described manner.

The second organic layer was prepared by weighing 5.0 parts by mass of a photopolymerization initiator (Irg184, manufactured by BASF SE) with respect to 95.0 parts by mass of an urethane bond-containing acrylate polymer (ACRIT 8BR930, manufactured by TAISEI FINE CHEMICAL CO, LTD.) and dissolving these in methyl ethyl ketone to obtain a coating solution having a concentration of solid contents of 15% by mass.

A surface of the inorganic layer of the laminated film was directly coated with this coating solution using a die coater according to a roll-to-roll system and was allowed to pass through a drying zone at an ambient temperature of 100° C. for 3 minutes. Thereafter, the laminated film coated with the coating solution and then dried was wound around a heat roller heated to a surface temperature of 60° C., irradiated (integrated irradiation quantity of approximately 600 mJ/cm²) with ultraviolet rays to be cured, and wound up. The thickness of the second organic layer formed on the inorganic layer of the laminated film as described above was 1 μm.

In this manner, a barrier film having the first organic layer, the inorganic layer, and the second organic layer on the support in this order was prepared.

<Preparation of Coating Solution for Wavelength Conversion Layer>

The following quantum dot-containing polymerizable composition A was prepared, filtered using a polypropylene filter with a pore diameter of 0.2 μm, dried under reduced pressure for 30 minutes, and used as a coating solution for a wavelength conversion layer. The concentration of the quantum dot in the following toluene dispersion liquid was 1% by mass.

Quantum dot-containing polymerizable composition A (coating solution for wavelength conversion layer) Toluene dispersion liquid of quantum dot 1 (maximum 10.0 parts by mass emission wavelength: 520 nm) Toluene dispersion liquid of quantum dot 2 (maximum  1.0 part by mass emission wavelength: 620 nm) Lauryl methacrylate 80.8 parts by mass Trimethylolpropane triacrylate 18.2 parts by mass Photopolymerization initiator (IRGACURE 819  1.0 part by mass (manufactured by BASF SE))

As the toluene solution of the quantum dot 1, a green quantum dot dispersion liquid CZ520-100 (manufactured by NN-LABS, LLC) having an emission wavelength of 520 nm was used. Further, as the toluene solution of the quantum dot 2, a red quantum dot dispersion liquid CZ620-100 (manufactured by NN-LABS, LLC) having an emission wavelength of 620 nm was used. These were both quantum dots in which CdSe was used as a core, ZnS was used as a shell, and octadecylamine was used as a ligand and dispersed in toluene at a concentration of 3% by mass.

<Preparation of Wavelength Conversion Member>

A wavelength conversion member formed by interposing a wavelength conversion layer between a first film and a second film was obtained by using the barrier films prepared by performing the above-described procedures as the first film and the second film. Specifically, a surface of the second organic layer was coated with the quantum dot-containing polymerizable composition A prepared in the above-described manner using a die coater while the first film was continuously transported at a tension of 1 m/min and then a tension of 60 N/m to form a coated film having a thickness of 50 μm. Next, the first film on which the coated film had been formed was wound around a backup roller, the second film was laminated on the coated film at an orientation at which the surface of the second organic layer was brought into contact with the coated film, and the laminate was continuously transported in a state in which the coated film was interposed between the first film and the second film and allowed to pass through a heating zone at 100° C. for 3 minutes. Thereafter, the laminate was irradiated with ultraviolet rays using an air-cooled metal halide lamp (manufactured by EYE GRAPHICS CO., LTD.) having a laser intensity of 160 W/cm, and the coated film of the quantum dot-containing polymerizable composition A was cured to form a wavelength conversion layer containing quantum dots. The irradiation quantity of ultraviolet rays was 2000 mJ/cm². The thickness of the wavelength conversion layer formed by being cured was approximately 50 μm. In this manner, a wavelength conversion member formed by interposing the wavelength conversion layer between two sheets of barrier films was obtained.

Example 13

An acrylic film having a thickness of 20 μm was used as a light guide plate in place of an acrylic plate having a thickness of 2 mm in Example 12. A backlight unit of Example 13 was prepared in the same manner as in Example 12 except for this point. Since the light guide plate was made thin, a backlight unit which was extremely thin as a whole was able to be realized.

Comparative Example 5

The perforated reflective plate E-A formed of only a multilayer film obtained by removing the silver reflection film 1 from the perforated reflective plate E-1A in Example 12 was used. A backlight unit of Comparative Example 5 was prepared in the same manner as in Example 12 except that the perforated reflective plate E-A was used and a linearly polarized light reflection film was used in place of the circular polarization reflection film in Example 12.

The front luminance was measured and evaluated in the following manner with those prepared in the examples and comparative examples in the above-described manners.

A backlight portion in a commercially available liquid crystal display device (AL2216W, manufactured by Acer Incorporated) obtained by using twisted nematic (TN) type liquid crystal cells was replaced by those of Examples 1 to 13 and Comparative Examples 1 to 5. White display was performed using this liquid crystal display device and the luminance was measured in each display.

Specifically, the front luminance was measured in a state in which white display was performed by the liquid crystal display device of each example left in a room under conditions of 25° C. and 60% RH using a measuring device (EZ-Contrast 160D, manufactured by ELDIM Co., Ltd.).

The configurations and the evaluation results of Examples 1 to 11 and Comparative Examples 1 to 4 were collectively listed in Table 1. Further, the configurations and the evaluation results of Examples 12 and 13 and Comparative Example 5 were collectively listed in Table 2.

The front luminance was evaluated as follows using the front luminance of Comparative example 3 as a reference in Table 1 and using the front luminance of Comparative example 5 as a reference in Table 2.

AA: 150% or greater of the front luminance of the reference

A: 140% or greater of the front luminance of the reference

B: 125% or greater and less than 140% of the front luminance of the reference

C: 115% or greater and less than 125% of the front luminance of the reference

D: 105% or greater and less than 115% of the front luminance of the reference

E: 95% or greater and less than 105% of the front luminance of the reference

F: less than 95% of the front luminance of the reference

In evaluation of the thickness, a case where an acrylic plate having a thickness of 2 mm was used as a light guide plate was evaluated as good, a case where an acrylic film having a thickness of 20 μm was used was evaluated as excellent, and a case where an interval of 10 mm was required without using a light guide plate was evaluated as poor.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Structure Polarized light reflection film Circular Circular Circular Circular Circular Circular Circular Circular of polarization polar- polar- polar- polarization polarization polarization polarization backlight reflection ization ization ization reflection reflection reflection reflection unit film 1 reflection reflection reflection film 1 film 1 film 2 film 1 (linearly film 1 film 1 film 1 (linearly polarized polarized light light reflection reflection film + λ/4 layer +λ/ film) 4 film applied to reflective plate) Perforated Structure E-1A P-2A P-3A P-1B P-2B (white P-1C (white E-1A E-1A reflective (multilayer (white (white (white PET + PET + silver plate film + silver PET + PET + PET + silver reflection reflection silver silver silver reflection film 1) film 1) reflection reflection reflection film 2) film 2) film 3) film 1) Reflectivity on 99% 99% 99% 99% 99% 99% 99% 99% viewing side Reflectivity on 99% 99% 99% 99% 99% 99% 99% 99% light source side Depolarization  4% 30% 60%  4% 30%  4%  4%  4% degree on viewing side Depolarization 95% 95% 95% 95% 95% 95% 95% 95% degree on light source side Opening ratio 10% 10% 10% 25% 25% 50% 10% 10% — — — — — — — — Light guide plate Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic plate Acrylic plate plate plate plate plate plate plate Light source White LED White White White White LED White LED White LED White LED LED LED LED Rear-side reflective plate White PET White White White White PET White PET White PET ESR PET PET PET Evaluation Front luminance B C D C D D B A Thickness Good Good Good Good Good Good Good Good Comparative Comparative Comparative Comparative Example 9 Example 10 Example 11 Example 1 Example 2 Example 3 Example 4 Structure Polarized light reflection film Circular Circular Circular None None Linearly Circular of polarization polarization polarization polarized polarization backlight reflection reflection reflection light reflection unit film 1 film 1 film 3 (λ/4 reflection film 1 layer + film cholesteric liquid crystal layer) Perfored Structure E-1A P-1AT (thick E-1A E-A E-A E-A P-4A (white reflective PET film + (multilayer PET + silver plate silver film) reflection reflection film 4) film 1) Reflectivity on 99% 99% 99% 99% 99% 99% 99% viewing side Reflectivity on 99% 99% 99% 99% 99% 99% 99% light source side Depolarization  4%  4%  4% 95% 95% 95% 70% degree on viewing side Depolarization 95% 95% 95% 95% 95% 95% 95% degree on light source side Opening ratio 10% 10% 10% 10% 10% 10% 10% Lens sheet — — — — — — Light guide plate Acrylic Acrylic plate Acrylic — Acrylic plate Acrylic plate Acrylic plate plate plate Light source White LED White LED White LED White LED White LED White LED White LED Rear-side reflective plate White PET White PET White PET ESR ESR ESR White PET Evaluation Front luminance AA AA B F F Reference E Thickness Good Good Good Poor Good Good Good

TABLE 2 Comparative Example 12 Example 13 Example 5 Structure of Polarized light reflection film Circular Circular Linearly backlight unit polarization polarization polarized light reflection film 1 reflection film 1 reflection film (linearly polarized light reflection film + λ/4 film) Perforated Structure E-1A (multilayer E-1A E-A (multilayer reflective film + silver film) plate reflection film 1) Reflectivity on 99% 99% 99% viewing side Reflectivity on 99% 99% 99% light source side Depolarization  4%  4% 95% degree on viewing side Depolarization 95% 95% 95% degree on light source side Opening ratio 10% 10% 10% Light guide plate Acrylic plate Acrylic film Acrylic plate Wavelength Wavelength Wavelength conversion layer conversion layer conversion layer Light source Blue LED Blue LED Blue LED Rear-side reflective plate White PET White PET White PET Evaluation Front luminance B A Reference Thickness Good Excellent Good

As listed in Table 1 and Table 2, the front luminance of each example according to the present invention was D or higher, in other words, a front luminance of 105% or greater of the reference was obtained, and thus the effect of improving the luminance by using the configurations of the present invention was confirmed. Particularly in a case where the ratio between the thickness of the perforated reflective plate and the opening diameter was increased or the directivity of light emitted from fine holes of the perforated reflective plate was improved by disposing a lens in a hole as in Examples 9 and 10, the effect of improving the luminance was extremely high.

In the case where a light guide plate is not provided as in Comparative Example 1, a certain thickness is required in order to have a structure in which a constant interval between the rear-side reflective plate and the perforated reflective plate is maintained, and the thickness of the backlight unit is unlikely to be reduced, but a desired thickness can be achieved so that the backlight unit can be thinned in a case where a light guide plate is used.

EXPLANATION OF REFERENCES

10, 10A, 10B, 10C, 40, 50: backlight unit

12: rear-side reflective plate

12 a: reflection surface

14, 15: light source

16: light guide plate

16 a: end surface of light guide plate

16 b: first principal surface of light guide plate

16 c: second principal surface of light guide plate

20: perforated reflective plate

21: light guide plate-side reflection surface (light guide plate-side surface)

22: emission-side reflection surface (emission-side surface)

24: fine hole

24 a, 24 b: opening

30, 35: circular polarization reflection film

32: λ/4 film

34: linearly polarized light reflection film

36: circular polarization separation film

38: λ/4 film

39: backlight-side polarizing plate

42: lens sheet

44: lens portion

52: wavelength conversion layer

54: wavelength conversion material

L: light

L₁: first linearly polarized light

L₂: second linearly polarized light

L_(L): left circular polarization

L_(R): right circular polarization 

What is claimed is:
 1. An edge light type backlight unit comprising: a light source; a light guide plate which has an end surface, on which light emitted from the light source is incident, and propagates the light incident from the end surface; a rear-side reflective plate which is disposed on a first principal surface side of the light guide plate; a perforated reflective plate which is disposed on a second principal surface side of the light guide plate facing the first principal surface so as to face the rear-side reflective plate and has a plurality of fine holes, which penetrate from a light guide plate-side surface to an emission-side surface facing the light guide plate-side surface and transmit light, and in which both the light guide plate-side surface and the emission-side surface are reflection surfaces and a depolarization degree of the emission-side surface is 60% or less; and a circular polarization reflection film which is disposed on the emission-side surface side of the perforated reflective plate, wherein the depolarization degree of the light guide plate-side surface of the perforated reflective plate is 90% or greater, and wherein at least the light guide plate-side surface of the perforated reflective plate consists of white polyethylene terephthalate.
 2. The edge light type backlight unit according to claim 1, wherein the emission-side surface of the perforated reflective plate is a specular reflection surface.
 3. The edge light type backlight unit according to claim 1, wherein an area ratio of openings of the fine holes in the emission-side surface of the perforated reflective plate is in a range of 10% to 50%.
 4. The edge light type backlight unit according to claim 1, wherein a ratio of a thickness of the perforated reflective plate to an opening diameter of the fine holes in the emission-side surface of the perforated reflective plate is 2 or greater.
 5. The edge light type backlight unit according to claim 1, wherein the openings of the fine holes of the perforated reflective plate on the light guide plate-side surface respectively have a lens.
 6. The edge light type backlight unit according to claim 1, wherein the circular polarization reflection film is formed of a λ/4 film and a linearly polarized light reflection film which are disposed in order from the perforated reflective plate side.
 7. The edge light type backlight unit according to claim 1, wherein the circular polarization reflection film includes a cholesteric liquid crystal layer.
 8. The edge light type backlight unit according to claim 1, wherein a wavelength conversion layer which receives light from the light source and emits light having a wavelength different from that of the light is provided between the light source and the perforated reflective plate. 